This invention relates to a method for recognizing rejection of transplanted hearts. The invention relates in particular, but not exclusively; to cardiac implants for detecting and alerting a patient to rejection of a transplanted heart.
After a human heart transplantation, it is necessary to monitor the recipient's body reaction against the implanted heart to prevent destruction of the new heart by an immune reaction. Commonly employed methods for detecting rejection are cumbersome and invasive. It is known that the morphology of cardiac electrograms alters during a rejection process, although this observation has not hitherto found practical use. For practical reasons, the preferred method of monitoring the cardiac electrogram would be by use of an implanted pacemaker which would be able to transmit the electrogram via telemetry to an external device such as a tape recorder or a paper recorder. The main limitation of this method lies in the poor transmission properties of the pacemaker electrocardiogram amplifier and the weakness of the telemetry link to the outside world.
More specifically, current pacemaker sensing amplifiers are relatively unsophisticated in the detection of intracardiac signals, relying entirely upon simple amplitude and frequency band pass filtration analysis.
For technical reasons, it is difficult to improve on the transmission properties of the electrogram of a pacemaker. Thus, the extraction of information about changes in the electrogram must be done inside the pacemaker before transmission to the external equipment takes place. To do this efficiently in an implantable system is only possible if there exists a simple and powerful algorithm by which relevant information about the signal morphology can be obtained.